Magnetron type amplifier



Dec. 3, 1963 w. HAss 3,113,239

MAGNETRON TYPE AMPLIFIER Filed June 16, 1960 2 Sheets-Sheet 1 .Hl y l VlA/ tu 7%5f J /V 7 70 y fr I I4 gy/ f4 ,/7' N35 /2 wwf/W Dec. 3, 1963 w.HAss 3,113,239

MAGNETRON TYPE AMPLIFIER Filed June 16, 1960 2 Sheets-Sheet 2 UnitedStates Patent 3,113,239 MAGNE'IRON TYPE AMPLIFIER Walter Hass, Freiburgim Breisgau, Germany, assignor to MWAG Mikrowellen A.G., Basel,Switzerland Filed June 16, 1969, Ser. No. 36,522 Claims priority,application Germany June 16, 1959 3 Claims. (Cl. S15-39.77)

This invention relates to a travelling-field magnetron constructed as anamplifying tube.

A special form of this category of tubes, one that starts from the usualform of the strapped magnetron, has become known by the designationPlatinotron See, for example, the article entitled Description andOperating Characteristics of the Platinotron by W. C. Brown in theProceedings of the IRE 1957, page 1209. It is distinguished from anordinary strapped magnetron by the fact that the sequence of resonatorsarranged concentrically around the cathode is severed with respect tohigh frequency at one place, and the beginning and end of the separatedresonator sequence receive in each case, by Way of the likewiseseparated phase rings (straps), a highfrequency conducting connection.The phase-ring conductor periodically loaded with the resonators thusacquires, with suitable electrical dimensioning, the character of adelay line or band-pass conductor, andthe magnetron, hus modified,acquires the character of a wide-band ampli- Now it is known thatstrapped magnetrons and their modifications can only be employed forwave lengths of more than about 3 centimetres. For smaller wave lengthsthe phase rings no longer admit of being manufactured with sufficientexactitude. For the range of wave lengths below 3 centimetres theso-called Rising Sun form has been adopted, which indeed, with respectto the stabilising of the 11F-mode, completely replaces the function ofthe phase rings, but does not immediately appear suited for theconstruction of a band-pass conductor. Hence only tubes of the nature ofthe Platinotron have hitherto been known for wave lengths far above thecritical wave length range of 3 centimetres.

This invention shows a way to manufacture amplify ing tubes of themagnetron construction for the range of shorter wave lengths also. Itmakes use of the possibility of replacing the phase rings by a tubularconductor or wave-guide.

The adoption of a wave-guide as a phase conductor in the magnetron isalready known as disclosed in German Patent 839,950. It was proposed toplace a rectangular Wave-guide concentrically around or co-axiallybeside the magnetron anode, and to couple it with the anode oscillatoryspaces by means of a slit. In that case, however, the wave-guide forms aclosed ring which is not severed with respect to high frequency waveenergy because those waves can propagate continuously around and aroundthe ring. That arrangement is intended to stabilize the 1rmode in thenormal magnetron and, therefore, does not suggest the idea of operatingthe magnetron as a wider band amplifier.

The main difficulty that stands in the way of employing a wave-guide inthe amplifying magnetron resides in the requirement of suiicientagreement between the angular velocity of the wave-guide wave and thatof the stream of electrons, It has hitherto seemed that this requirementcould not readily be fulfilled, since the phase velocity of thewave-guide wave is greater than the Velocity of light, whereas withinthe scope of the practically controllable operative voltages, the speedof flow of the electrons is less by about one order of magnitude.

The subject of this invention is an amplifying tube of the magnetrontype, with a cathode, and having resonators axially symmetricallyarranged in relation to the axis of ICC the cathode, the resonatorsbeing surrounded by a waveguide ring. It is characterized by the featurethat the wave-guide ring is severed at one place with respect to highfrequency and is provided with high-frequency supply leads, and that theresonators are coupled to the wave-guide ring individually by way ofsuch a long radial coupling path that the angular velocities of thewaved guide wave and of the electron wave are equal.

By this arrangement the wave of the wave-guide is transmitted to acircuit path located nearer to the cathode. The phase velocity istherefore transformed, in proportion to the diameter of the path, and isin this way adapted to readily realizable operative data.

What is particularly advantageous is the electrical decoupling betweenthe high-frequency supply leads (input and output), in the case of theamplifier tube shown in FIG. 1, by means of a metallic transversepartition in the wave-guide. lt must here be emphasized that such aseparation constitutes a simpler and more reliable measure for avoidingundesirable external reaction than is possible with the use of straps.

With respect to the necessary band-pass character of the wave-guidering, the resonators, coupled to the waveguide ring, of the actualmagnetron system are to be constructed as sections, open towards thecathode, of Lecher conductors or wave-guides with a series-resonancecharacter. These resonators, the centre lines of which, in the axis ofthe wave-guide ring for example, are at a distance of about M4 from oneanother, therefore solve a twofold problem: on the one hand they formthe series-coupled series oscillatory circuits that are necessary in thesense of the band-pass character of the ring conductor, and they alsoform the medium of the alternating action between the flow of electronsand the wave-guide ring which is required for the functioning as anamplifying tube.

In order to adapt the necessary radial distance between the wave-guidering and the segment heads to the desired operative conditions of thetube, it may be advantageous to increase the electrical length oftheresonators by single or multiple amounts of M2. A particularlyadvantageous kind of construction is however characterized by thefeature that between the resonator and the wave-guide ring specialwave-guide sections are interposed, which are preferably directedradially to the axis of the cathode. Their length should amount to atleast about a quarter of the wave length.

The adaptation of the radial distance between the waveguide ring and theresonator heads is advantageously facilitated by these strappings orcoupling conductors being given an inclined or curved course, deviatingfrom the radial direction. An advantageous construction of thestrappings consists in constructing them as flat rectangular wave-guidesections terminating in slots in the guidebeam plane of the wave-guidering and coupling slots in the resonators, the shorter cross-sectionalside of the said sections being selected, in a manner known in itself,to supply the required impedance match between the resonator and thewave-guide.

The abovementioned electrical separation between input and output mustalso be carried out within the sequence of resonators. It isadvantageous to utilize for this purpose the peripheral range that isclaimed by the input and output lines. In this sector, which isnecessarily free from coupling slots, the resonators are constructed ashigh-frequency separation of the resonator sequence. This isadvantageously effected in such a way that the resonators arranged hereare de-tuned in relation to the useful-wave range, or else are partlyreplaced by solid electrodes. In this case a resonator which is notdetuned, arranged for instance in the middle of the separating sector,may be given a high-frequency supply lead of its own, by means of whichthe functioning of the tube is controlled. This resonator mayalternatively be replaced by an electrode with a simple supply lead. Itis likewise utilized for the control, by means of direct voltage orlow-frequency voltage.

The space required on the wave-guide parting place for the inward andoutward lead wires, in which space are also included means known inthemselves for diminishing the reflection loss due to impedancediscontinuity, can be rendered unnecessary by placing the wave-guidering in the form of one or more helical turns around the inner system.This arrangement has the advantage that the inward conductors areparticularly simple in shape and free from such discontinuity.

One constructional example of the invention is illus trated in theaccompanying drawings, in which:

FIGURE 1 shows the tube in a central section perpendicular to the axisof the cathode; and

FIGURE 2 is a section on the line A-B in FIGURE 1.

In these gures, 1 is the metallic magnetron body, usually made ofcopper, with the wave-guide ring 2, the coupling conductors orstrappings 3, the resonators 4 and the cathode 5. The wave-guide ring 2is interrupted by the transverse metallic partition 6. The input andoutput of the tube are formed by the wave-guides or hollow conductors 7and 8 and 7 and 8 respectively and the vacuum-tight apertures 9 and 9.Wedges 10 and 11 serve in a known manner for constituting a su'icientlyshock-free transition. The strappings 3 are produced by slots in theotherwise solid ring 12. The parting place within the resonator ring isformed by a solid body 13, with adjacent de-tuned cavities 14.

The magnet arrangements necessary for operating the tube are notrepresented in the drawing or described in the speciiication, since theyare immaterial to the description of the invention, being structuralelements of the magnetron that are known to the technologist.

The application of this invention is not restricted to wave lengthsbelow 3 centimetres.

I claim:

1. A traveling Wave magnetron amplifier comprising an evacuatedstructure enclosing a cathode and an anode, the anode being arrangedabout the cathode to provide a circular interelectrode space, the anodehaving a plurality of resonators contiguous to the interelectrode space,electrons emitted by the cathode being caused to move in theinterelectrode space, a waveguide surrounding the reso- 5 nators, thewaveguide having signal input and output terminals formed by straightwaveguide sections, the straight sections having a common metallic wallextending radially outwards from the inner circumferential wall of thewaveguide, and means forming signal coupling paths from the waveguide tothe resonators, the paths being of such length as to equalize theangular velocity of an electron Wave in the interelectrode space and anelectromagnetic wave propagating through the waveguide.

2. A traveling wave magnetron amplifier comprising an evacuatedstructure enclosing a cathode and an anode, the anode being arrangedabout the cathode to provide a circular interelectrode space, the anodehaving a plurality of resonators contiguous to the interelectrode space,electrons emitted from the cathode being caused to move 0 in theinterelectrode space, a main waveguide surrounding the resonators, themain waveguide having separate input and output ports, and means formingsignal coupling paths from the main waveguide to the resonators, eachpath being formed by a waveguide section interconnecting the resonatorand the main waveguide, and each section being an integral multiple of aquarter wave length at the signal frequency.

3. An amplier in accordance with claim 2 in which the waveguide sectionacts to match the impedance of the 30 main waveguide to that of theresonator.

References Cited in the tile of this patent UNITED STATES PATENTS OTHERREFERENCES Description and Operating Characteristics of the Platination,(Brown), Institution of Radio Engineers (Proceeding), 1957, pages 1209to 1222 relied on.

1. A TRAVELING WAVE MAGNETRON AMPLIFIER COMPRISING AN EVACUATEDSTRUCTURE ENCLOSING A CATHODE AND AN ANODE, THE ANODE BEING ARRANGEDABOUT THE CATHODE TO PROVIDE A CIRCULAR INTERELECTRODE SPACE, THE ANODEHAVING A PLURALITY OF RESONATORS CONTIGUOUS TO THE INTERELECTRODE SPACE,ELECTRONS EMITTED BY THE CATHODE BEING CAUSED TO MOVE IN THEINTERELECTRODE SPACE, A WAVEGUIDE SURROUNDING THE RESONATORS, THEWAVEGUIDE HAVING SIGNAL INPUT AND OUTPUT TERMINALS FORMED BY STRAIGHTWAVEGUIDE SECTIONS, THE STRAIGHT SECTIONS HAVING A COMMON METALLIC WALLEXTENDING RADIALLY OUTWARDS FROM THE INNER CIRCUMFERENTIAL WALL OF THEWAVEGUIDE, AND MEANS FORMING SIGNAL COUPLING PATHS FROM THE WAVEGUIDE TOTHE RESONATORS, THE PATHS BEING OF SUCH LENGTH AS TO EQUALIZE THEANGULAR VELOCITY OF AN ELECTRON WAVE IN THE INTERELECTRODE SPACE AND ANELECTROMAGNETIC WAVE PROPAGATING THROUGH THE WAVEGUIDE.